阅读说明：本技术 放射线检测装置 (Radiation detecting apparatus ) 是由 大田良亮 于 2018-06-19 设计创作，主要内容包括：本发明的放射线检测装置(1A),由：闪烁器(11)；检测来自闪烁器(11)的闪烁光,并且输出检测信号的光检测器(15)；比较第一阈值电压(V1)和检测信号,并且输出具有第一时间宽度(T1)的信号的第一比较器(21)；测量第一时间宽度(T1)的第一时间宽度测量器(23)；比较第二阈值电压(V2)和检测信号,并且输出具有第二时间宽度(T2)的信号的第二比较器(22)；测量第二时间宽度(T2)的第二时间宽度测量器(24)；以及基于第一、第二时间宽度(T1、T2),并且求得表示检测信号的时间波形的时间常数(τ)的解析部(30)构成。由此,实现能够适当地取得、判别从包含闪烁器和光检测器的放射线检测装置输出的检测信号的时间波形信息。(A radiation detection device (1A) of the present invention comprises: a scintillator (11); a photodetector (15) that detects scintillation light from the scintillator (11) and outputs a detection signal; a first comparator (21) that compares the first threshold voltage (V1) and the detection signal and outputs a signal having a first time width (T1); a first temporal width measurer (23) that measures a first temporal width (T1); a second comparator (22) that compares the second threshold voltage (V2) with the detection signal and outputs a signal having a second time width (T2); a second time width measurer (24) that measures a second time width (T2); and an analysis unit (30) for obtaining a time constant (τ) indicating a time waveform of the detection signal based on the first and second time widths (T1, T2). Thus, time waveform information of a detection signal output from a radiation detection apparatus including a scintillator and a photodetector can be appropriately acquired and discriminated.)

1. A radiation detecting apparatus is characterized in that,

the disclosed device is provided with:

a scintillator that generates scintillation light in response to incidence of radiation;

a photodetector that detects the scintillation light output from the scintillator and outputs a detection signal;

a first comparator that compares a first threshold voltage with the detection signal and outputs a first digital signal having a first time width corresponding to a time when a voltage value of the detection signal exceeds the first threshold voltage;

a first time width measurer that measures the first time width of the first digital signal;

a second comparator that compares a second threshold voltage different from the first threshold voltage with the detection signal and outputs a second digital signal having a second time width equivalent to a time when a voltage value of the detection signal exceeds the second threshold voltage;

a second time width measurer measuring the second time width of the second digital signal; and

and an analysis unit configured to obtain a time constant indicating a time waveform of the detection signal based on the first time width and the second time width.

2. The radiation detecting apparatus according to claim 1,

the scintillator includes a first scintillator portion that generates scintillation light having a predetermined time waveform and a second scintillator portion that generates scintillation light having a different time waveform from the first scintillator portion.

3. The radiation detecting apparatus according to claim 2,

the analysis unit determines whether or not the detection signal is a detection signal that is output from the photodetector and is caused by scintillation light generated in either one of the first scintillator unit and the second scintillator unit, based on the time constant.

4. The radiation detecting apparatus according to any one of claims 1 to 3,

the photodetector includes a first photodetector that outputs a detection signal having a predetermined time waveform, and a second photodetector that outputs a detection signal having a time waveform different from that of the first photodetector.

5. The radiation detecting apparatus according to claim 4,

the analysis unit determines whether or not the detection signal is a detection signal output from one of the first light detection unit and the second light detection unit based on the time constant.

6. The radiation detecting apparatus according to any one of claims 1 to 5,

each of the first time width measurer and the second time width measurer includes a time-to-digital converter.

7. The radiation detecting apparatus according to any one of claims 1 to 6,

a condition is satisfied that a rise time τ r in a time waveform of the detection signal satisfies a fall time τ d

(τr/τd)<0.1。

8. The radiation detecting apparatus according to any one of claims 1 to 7,

the analysis unit passes the first threshold voltage V1, the first time width T1, the second threshold voltage V2, and the second time width T2

τ＝(T1-T2)/log(V2/V1)

And obtaining the time constant tau.

9. The radiation detecting apparatus according to any one of claims 1 to 8,

the analysis unit obtains a peak value in a time waveform of the detection signal based on the time constant.

Technical Field

The present invention relates to a radiation detection apparatus for detection of radiation.

Background

In a Positron Emission Tomography (PET) apparatus, a substance labeled with a Radioisotope (RI) that emits positrons (Positron) toward a subject is injected as a tracer. Then, a pair of γ rays generated by extinguishing the positron emitted from the RI substance and the electron mound in the normal substance are measured in the radiation detector, and information on the subject is acquired.

A radiation detector used for detecting radiation such as gamma rays in such a measurement device such as a PET device can be suitably configured by combining a scintillator that generates scintillation light in accordance with incidence of radiation and a photodetector that detects the scintillation light and outputs a detection signal, for example (see patent document 1, for example).

Disclosure of Invention

Technical problem to be solved by the invention

In a radiation detector used in a PET apparatus, it is important to know at which position a gamma ray incident on the detector interacts with a scintillator and is detected. In particular, when a gamma ray is detected at a peripheral position of a field of view of the detector (a position distant from the center), there is a problem that a Parallax Error (paralax Error) occurs, and thereby the spatial resolution of the gamma ray is lowered. In order to prevent such a decrease in spatial resolution of radiation detection, a Phoswich type detector has been proposed.

In a Phoswich-type radiation detector, a scintillator for detecting radiation is configured by superimposing 2 types of scintillator portions having different time constants from detection signals. In such a configuration, the time waveform information of the detection signal can be used to determine which scintillator portion has detected radiation, for example, based on the time constant of the time waveform. The Phoswich type detector can be used as a doi (depth of interaction) detector.

As a method of obtaining a parameter indicating a time waveform such as a time constant of a detection signal output from a detector, for example, a configuration of sampling a waveform of a time waveform of a detection signal may be considered. However, in the configuration in which waveform sampling of the detection signal is performed, a large amount of information of the detection signal is obtained, but it is not suitable for radiation measurement at a high count rate, and there is a problem that it is difficult to reduce power consumption.

Patent document 2 and non-patent document 1 describe a configuration in which a Threshold voltage is compared with a detection signal, and a Time (ToT: Time over Threshold) at which the voltage value of the signal exceeds the Threshold voltage is determined. However, even in these configurations, the time constant itself of the detection signal is not obtained, and it is difficult to discriminate the time waveform of the detection signal with sufficient accuracy. The problem of acquiring and determining the time waveform information of the detection signal as described above occurs similarly in radiation other than the above-described Phoswich type detector.

The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a radiation detection apparatus capable of appropriately acquiring and discriminating time waveform information of a detection signal output from a radiation detector including a scintillator and a photodetector.

Means for solving the problems

According to the radiation detection apparatus of the present invention, there is provided: (1) a scintillator that generates scintillation light in response to incidence of radiation; (2) a photodetector that detects scintillation light output from the scintillator and outputs a detection signal; (3) a first comparator that compares the first threshold voltage with the detection signal and outputs a first digital signal having a first time width corresponding to a time during which a voltage value of the detection signal exceeds the first threshold voltage; (4) a first time width measurer which measures a first time width of the first digital signal; (5) a second comparator that compares a second threshold voltage different from the first threshold voltage with the detection signal and outputs a second digital signal having a second time width equivalent to a time during which a voltage value of the detection signal exceeds the second threshold voltage; (6) a second time width measurer measuring a second time width of the second digital signal; and (7) an analysis unit configured to obtain a time constant indicating a time waveform of the detection signal based on the first time width and the second time width.

In the above-described radiation detection apparatus, a first comparator and a second comparator, in which different threshold voltages are set, are provided for a detection signal output from a radiation detector including a scintillator and a photodetector. Then, the different time widths of the first and second digital signals outputted from the 2 comparators are measured by the first and second time width measuring devices, and based on the obtained first time width and second time width, a parameter indicating a time waveform of the detection signal corresponding to the detection of the radiation, i.e., a time constant is obtained. With such a configuration, the time waveform information of the detection signal can be appropriately acquired and discriminated with a simple configuration.

ADVANTAGEOUS EFFECTS OF INVENTION

According to the radiation detection apparatus of the present invention, the first and second comparators having different threshold voltages set in relation to the detection signal output from the radiation detector including the scintillator and the photodetector are provided, the time widths of the first and second digital signals output from the comparators are measured by the first and second time width measuring devices, and the time constant representing the time waveform of the detection signal is obtained based on the obtained first and second time widths, whereby the time waveform information of the detection signal can be appropriately acquired and discriminated with a simple configuration.

Drawings

Fig. 1 is a diagram schematically showing a configuration of a first embodiment of a radiation detection apparatus.

Fig. 2 is a flowchart illustrating a radiation detection method in relation to the detection apparatus shown in fig. 1.

Fig. 3 is a graph showing a time waveform with respect to a detection signal output from the photodetector.

Fig. 4 is a graph showing first and second time widths with respect to a detection signal.

Fig. 5 is a graph showing a rise time and a fall time of a time waveform of scintillation light output from the scintillator.

Fig. 6 is a diagram showing a configuration of a PET apparatus using the detection apparatus shown in fig. 1.

Fig. 7 is a diagram schematically showing the configuration of a second embodiment of the radiation detection apparatus.

Fig. 8 is a flowchart illustrating a radiation detection method in relation to the detection apparatus shown in fig. 7.

Fig. 9 is a diagram illustrating a measurement experiment performed with respect to the radiation detector illustrated in fig. 7.

Fig. 10 is a graph showing a time waveform and first and second time widths of the detection signal obtained in the measurement experiment shown in fig. 9.

Fig. 11 is a graph showing the discrimination of the scintillator section with respect to the time constant of the detection signal obtained in the measurement experiment shown in fig. 9.

Fig. 12 is a view schematically showing the configuration of a third embodiment of the radiation detection apparatus.

Fig. 13 is a plan view showing the structure of a photodetector in the detection device shown in fig. 12.

Fig. 14 is a plan view partially enlarged showing the structure of the photodetector shown in fig. 13.

Fig. 15 is a flowchart illustrating a radiation detection method in relation to the detection apparatus shown in fig. 12.

Fig. 16 is a diagram schematically showing a configuration of a first modification of the photodetector in the detection device shown in fig. 12.

Fig. 17 is a diagram schematically showing a configuration of a second modification of the photodetector in the detection device shown in fig. 12.

Detailed Description

Hereinafter, embodiments of the radiation detection apparatus according to the present invention will be described in detail with reference to the accompanying drawings. In the description of the drawings, the same elements are denoted by the same reference numerals, and redundant description is omitted. In addition, the dimensional ratios in the drawings do not necessarily have to coincide with the illustrated dimensional ratios.

Fig. 1 is a diagram schematically showing a configuration of a first embodiment of a radiation detection apparatus. The radiation detection apparatus 1A according to the present embodiment includes a radiation detector 10, a time waveform measuring unit 20, and an analyzing unit 30.

The radiation detector 10 detects incident radiation, and outputs the generated electric signal (voltage signal) as a detection signal. The radiation detector 10 in the present configuration example has a scintillator 11 and a photodetector 15. The scintillator 11 is made of a predetermined scintillator material, and generates scintillation light in response to incidence of radiation to be detected. The temporal waveform of the scintillation light generated in the scintillator 11 is a predetermined waveform determined in accordance with the light emission characteristics of the scintillation material. The radiation detected by the scintillator 11 is, for example, γ rays, X rays, electrons, charged particles, cosmic rays, or the like.

The photodetector 15 detects scintillation light output from the scintillator 11 and outputs a detection signal. As the photodetector 15, for example, a Photomultiplier Tube (PMT), a SiPM (silicon Photomultiplier), an MPPC (Multi-Pixel Photon Counter), or the like can be used. When the output from the photodetector 15 is a current signal, it is preferable that the current-voltage conversion be performed by an amplifier or the like to generate a detection signal as a voltage signal. The time waveform of the detection signal is a predetermined waveform determined based on the time waveform of the scintillation light, the light detection characteristics of the photodetector 15, and the like. The detection signal S0 generated by the photodetector 15 is output from the output terminal 16 to the subsequent time waveform measuring unit 20.

The time waveform measuring unit 20 is a measuring circuit unit that measures a time waveform of the detection signal S0 output from the output terminal 16 of the photodetector 15. The time waveform measuring unit 20 in the present configuration example includes a first comparator 21, a second comparator 22, a first time width measuring device 23, and a second time width measuring device 24. The detection signal S0 output from the photodetector 15 is branched at a branch point 17, and the branched detection signals S0 are input to the first comparator 21 and the second comparator 22, respectively.

The first comparator 21 is given a first threshold voltage V1. The first comparator 21 compares the first threshold voltage V1 with the detection signal S0 as a voltage signal, and outputs a first digital signal S1 having a first time width T1 corresponding to a time when the voltage value of the detection signal S0 exceeds the threshold voltage V1. In addition, the second comparator 22 is given a second threshold voltage V2 having a voltage value different from the first threshold voltage V1. The second comparator 22 compares the second threshold voltage V2 with the detection signal S0, and outputs a second digital signal S2 having a second time width T2 corresponding to a time during which the voltage value of the detection signal S0 exceeds the threshold voltage V2.

The first time width measuring device 23 measures the first time width T1 of the first digital signal S1 output from the first comparator 21, and outputs the data of the obtained first time width T1 to the analysis unit 30 at the subsequent stage. The second time width measuring device 24 measures the second time width T2 of the second digital signal S2 output from the second comparator 22, and outputs the data of the obtained second time width T2 to the analysis unit 30. Each of the first Time width measurer 23 and the second Time width measurer 24 is preferably constituted by a Time-to-Digital Converter (TDC).

The analysis unit (analysis device) 30 obtains a time constant τ indicating a parameter that is a time waveform of the detection signal S0, based on the first time width T1 and the second time width T2 that are input from the first and second time width measuring instruments 23 and 24, respectively. The time constant τ is, for example, a fall time τ d in a time waveform of the detection signal S0 described later. The analysis unit 30 may obtain a parameter indicating a time waveform other than the fall time τ d as the time constant τ. The analysis unit 30 may further determine the peak value E in the time waveform of the detection signal S0 based on the time constant τ, if necessary. As the analysis unit 30, for example, a computer including a CPU, a memory, and the like, an FPGA (Field Programmable gate array), and the like can be used.

The analysis unit 30 is connected to a display unit (display device) 31 and a storage unit (storage device) 32. The display unit 31 displays the analysis result of the detection signal S0 from the analysis unit 30 such as the time constant τ derived as described above, as necessary. The storage unit 32 stores data of the first and second time widths T1 and T2 inputted to the analysis unit 30, data of the analysis result such as the time constant τ derived by the analysis unit 30, and the like.

Effects of the radiation detection apparatus 1A according to the above embodiment will be described.

In the radiation detection apparatus 1A shown in fig. 1, a first comparator 21 and a second comparator 22 are provided in which threshold voltages V1 and V2 different from each other are set with respect to a detection signal S0 output from a radiation detector 10 including a scintillator 11 and a photodetector 15. Then, the time widths of the first and second digital signals S1, S2 outputted from the 2 comparators 21, 22, which are different from each other, are measured by the first and second time width measuring devices 23, 24, and the time constant τ indicating the time waveform corresponding to the radiation detection signal S0 is obtained in the analysis unit 30 based on the obtained first time width T1 and second time width T2. With such a configuration, the time waveform information of the detection signal S0 can be appropriately acquired and determined with a simple configuration without performing waveform sampling or the like.

In the above-described detection device 1A, the analysis unit 30 may be configured to determine the peak value E in the time waveform of the detection signal S0 based on the time constant τ, in addition to the time constant τ. According to such a configuration, the peak value E of the detection signal S0 can be easily obtained at high speed and low power consumption without additionally providing a peak value measuring instrument such as an Analog-to-Digital Converter (ADC) in addition to the comparators 21 and 22 and the time waveform measuring unit 20 including the time width measuring units 23 and 24. Note that, such a peak value E may not be obtained if it is not necessary.

Fig. 2 is a flowchart illustrating a radiation detection method in relation to the radiation detection apparatus 1A illustrated in fig. 1. Fig. 3 is a graph showing a time waveform of the detection signal S0 output from the photodetector 15. Fig. 4 is a graph showing first and second time widths T1 and T2 obtained by applying the first and second threshold voltages V1 and V2 to the detection signal S0. Hereinafter, the radiation detection method according to the present embodiment will be described with reference to specific examples of the method of deriving the time waveform and the time constant τ of the detection signal S0.

In the radiation detection method shown in fig. 2, first, an radiation is detected in the radiation detector 10 constituted by the scintillator 11 and the photodetector 15, and a detection signal S0 corresponding to the incidence of the radiation is output from the output terminal 16 of the photodetector 15 (step S11). Fig. 3 schematically shows an example of a time waveform of the detection signal S0 output from the photodetector 15. In the graph of fig. 3, the horizontal axis represents time, and the vertical axis represents the voltage value of the detection signal S0.

In the time waveform of the detection signal S0 shown in fig. 3, a portion before the signal peak Sp is a rising signal portion Sr, and a portion after the signal peak Sp is a falling signal portion Sd. The time waveform of the detection signal S0 having the shape shown in fig. 3, for example, can be represented by the following expression (1).

[ formula 1]

Here, in equation (1), E represents a peak value which is a voltage value at the signal peak Sp, τ r represents a rising time (rising time constant) in the rising signal section Sr, and τ d represents a falling time (falling time constant) in the falling signal section Sd.

The detection signal S0 output from the radiation detector 10 is input to the first and second comparators 21 and 22 of the time waveform measuring unit 20. The first comparator 21 compares the first threshold voltage V1 with the detection signal S0, and outputs a first digital signal S1 having a first time width T1 corresponding to a time when the voltage value of the detection signal S0 exceeds the threshold voltage V1, as shown in the graph of fig. 4. The second comparator 22 compares the second threshold voltage V2 with the detection signal S0, and similarly outputs a second digital signal S2 having a second time width T2 corresponding to the time when the voltage value of the detection signal S0 exceeds the threshold voltage V2 (step S12). These first and second time widths T1, T2 are measured by the first and second time width measuring devices 23, 24, respectively (step S13).

In fig. 3 and 4, the case where the signal peak Sp in the time waveform of the detection signal S0 is located in the positive direction with respect to the voltage is shown, but when the signal peak Sp of the detection signal S0 is located in the negative direction with respect to the voltage, the time width described above may be determined, for example, as long as the time width corresponding to the time when the voltage value of the detection signal S0 in which the positive and negative of the detection signal are inverted exceeds the threshold voltage is obtained. This corresponds to the time when the voltage value of the original detection signal is below the threshold voltage.

The analysis unit 30 derives a time constant τ indicating the time waveform of the detection signal S0 based on the first and second time widths T1 and T2 measured by the first and second time width measuring instruments 23 and 24 (step S14). The analysis unit 30 derives a peak value E in the time waveform of the detection signal S0 based on the first and second time widths T1 and T2, the time constant τ, and the like as necessary (step S15).

Here, in the time waveform of the detection signal S0 output from the photodetector 15, when the rise time τ r is sufficiently short with respect to the fall time τ d, the first time width T1 of the detection signal S0 with respect to the first threshold voltage V1 is represented by the following expression (2).

[ formula 2]

The second time width T2 of the detection signal S0 with respect to the second threshold voltage V2 is similarly expressed by the following expression (3).

[ formula 3]

Therefore, when the time constant τ derived as the time waveform parameter in the analysis unit 30 is set to the fall time τ d in the time waveform of the detection signal S0, the time constant τ can be obtained by the following expression (4).

[ formula 4]

τ＝τ_d＝(T1-T2)/log(V2/V1) …(4)

By using the formula (4), the time constant τ of the detection signal S0 can be appropriately and easily obtained.

In the analysis unit 30, when the peak value E of the detection signal S0 is determined in addition to the time constant τ, the peak value E can be determined by the following equation (5) using the fall time τ d determined as the time constant τ.

[ formula 5]

The first and second threshold voltages V1 and V2 of the first and second comparators 21 and 22 may be arbitrarily set and adjusted to easily obtain the time constant τ and the like.

In addition, regarding the above-described waveform condition that the rise time τ r is sufficiently short with respect to the fall time τ d in the detection signal S0, specifically, for example, the condition of the rise time τ r with respect to the fall time τ d in the time waveform of the detection signal S0 is preferably satisfied

(τr/τd)<0.1。

Here, fig. 5 is a graph showing the rise time τ r and the fall time τ d of the time waveform of the scintillation light output from the scintillator. Fig. 5 shows a rise time τ r and a fall time τ d of a time waveform for LSO, LYSO, LaBr3, GSO, and GAGG, which are conventional scintillators used in PET apparatuses. For these scintillators, it is considered that the above condition that the rise time τ r is sufficiently short with respect to the fall time τ d is sufficiently satisfied.

The radiation detection apparatus 1A having the structure shown in fig. 1 can be suitably applied to, for example, a PET apparatus. Fig. 6 is a diagram showing a configuration of a PET apparatus to which the radiation detection apparatus shown in fig. 1 is applied. The PET apparatus 2A is configured such that a plurality of radiation detectors 10 including a scintillator 11 and a photodetector 15 are disposed so as to surround a subject P. Further, a signal processing section 60 including the time waveform measuring section 20 and the analyzing section 30 shown in fig. 1 is provided for the detection signal S0 output from each radiation detector 10.

In the PET apparatus 2A, a pair of γ rays generated by annihilation of positrons inside the subject P is detected by the plurality of radiation detectors 10. In the example shown in fig. 6, a pair of γ rays generated at a measurement point P1 inside the subject P is detected by the radiation detectors 101 and 102. In addition, the pair of γ rays generated at the measurement point P2 are detected by the radiation detectors 103 and 104.

The detection signal S0 output from the radiation detector 10 is input to the signal processing unit 60, and as described above with reference to fig. 1, the signal processing unit 60 measures the first and second time widths T1 and T2 of the detection signal S0, derives the time constant τ of the time waveform, and so forth. Further, based on the obtained time constant τ, characteristics of the radiation detector 10 such as characteristics of the scintillator 11 are derived. The derived information of the characteristics of the radiation detector 10 can be used, for example, for performance improvement of the PET apparatus 2A.

Fig. 7 is a diagram schematically showing the configuration of a second embodiment of the radiation detection apparatus. The radiation detection apparatus 1B according to the present embodiment includes a radiation detector 10B, a time waveform measuring unit 20, and an analyzing unit 30. Among these, the configurations of the time waveform measuring unit 20 and the analyzing unit 30 are the same as those shown in fig. 1. In fig. 7, the display unit 31 and the storage unit 32 connected to the analysis unit 30 are not shown.

The radiation detector 10B in the present configuration example includes a scintillator 11 and a photodetector 15. The scintillator 11 is configured by arranging the first scintillator portion 12 and the second scintillator portion 13 in this order from the photodetector 15 side.

The first scintillator portion 12 is made of a first scintillator material, and generates scintillation light having a predetermined time waveform in accordance with incidence of radiation. The second scintillator portion 13 is made of a second scintillator material different from the first scintillator material, and generates scintillation light having a time waveform different from that of the first scintillator portion 12 in accordance with incidence of radiation. The photodetector 15 detects scintillation light output from the first scintillator portion 12 or the second scintillator portion 13, and outputs a detection signal S0 via the output terminal 16 and the amplifier 18. At this time, the time waveform of the detection signal S0 output from the photodetector 15 has a different waveform depending on whether or not the radiation has interacted with any of the first and second scintillator portions 12 and 13.

Fig. 8 is a flowchart illustrating a radiation detection method carried out in relation to the radiation detection apparatus 1B illustrated in fig. 7. In the radiation detection method shown in fig. 8, first, an radiation is detected in the radiation detector 10B constituted by the scintillator 11 including the first and second scintillator sections 12, 13 and the photodetector 15, and a detection signal S0 is output from the output terminal 16 of the photodetector 15 (step S21).

The detection signal S0 is input to the first and second comparators 21 and 22 of the time waveform measuring unit 20 via the amplifier 18 and the branch point 17. The first comparator 21 compares the first threshold voltage V1 with the detection signal S0, and outputs a first digital signal S1 having a first time width T1. In addition, the second comparator 22 compares the second threshold voltage V2 with the detection signal S0, and outputs a second digital signal S2 having a second time width T2 (step S22). These first and second time widths T1, T2 are measured by the first and second time width measuring devices 23, 24, respectively (step S23).

The analysis unit 30 derives a time constant τ indicating the time waveform of the detection signal S0 based on the first and second time widths T1 and T2 measured by the first and second time width measuring instruments 23 and 24 (step S24). Based on the obtained time constant τ, the analysis unit 30 determines whether or not the detection signal S0 is a detection signal output from the photodetector 15 due to scintillation light generated in either one of the first scintillator unit 12 and the second scintillator unit 13, that is, whether or not radiation is detected in either one of the first scintillator unit 12 and the second scintillator unit 13 (step S25).

In the configuration in which the time constant τ of the detection signal S0 is obtained based on the first and second time widths T1 and T2 as described above, when the scintillator 11 includes the first and second scintillator units 12 and 13, it is possible to determine whether or not the radiation source is detected by any of the first and second scintillator units 12 and 13 based on the obtained time constant τ. In addition, as described above, the determination of the scintillator portion can be performed similarly even when the scintillator includes 3 or more scintillator portions.

A measurement experiment was performed for the determination of the scintillator section based on the time constant τ of the detection signal S0. Fig. 9 is a diagram illustrating a measurement experiment performed with respect to the radiation detector 10B illustrated in fig. 7. In the present measurement experiment, the radiation detector 10B was disposed in the constant temperature bath 35 at a temperature of 25 ℃. As for the structure of the radiation detector 10B, 5X 5mm is used³The GSO scintillator of (2) is a 3X 10mm scintillator used as the first scintillator 12³The second scintillator portion 13 is a GAGG scintillator.

In addition, S13360-3050 manufactured by Hamamatsu Photonics was used as the MPPC of the photodetector 15. The light receiving surface of the MPPC is 3.0 multiplied by 3.0mm²And the arrangement pitch of the plurality of light detection pixels arranged in two dimensions is 50 μm. In addition, for the voltage applied to MPPC, the voltage exceeding the breakdown voltage is divided into V_excess4.0V. Further, the scintillator 11 including the first and second scintillator portions 12 and 13 is disposed at a distance of 5cm from each other²²The Na source serves as the radiation source 36, and the radiation detector 10B detects γ rays from the radiation source 36.

In the present measurement experiment, the oscilloscope 38 is provided in place of the time waveform measuring unit 20 shown in fig. 7 for the detection signal S0 output from the output terminal 16 of the photodetector 15, the time waveform data measured by the oscilloscope 38 is acquired to the computer (PC) of the analyzing unit 30, and then the first and second time widths T1 and T2, the time constant τ, and the like of the time waveform of the detection signal S0 are analyzed by software. In addition, DSO-S404A manufactured by Keysight Corporation was used as the oscilloscope 38.

Fig. 10 is a graph showing a time waveform and first and second time widths T1, T2 with respect to the detection signal S0 obtained in the measurement experiment shown in fig. 9. Here, the analysis unit 30 performs fitting to the time waveform data S6 of the detection signal S0 obtained by the oscilloscope 38 by a theoretical equation, and obtains a time waveform S7 as a result of the fitting. The time waveform S7 is numerically analyzed with the first and second threshold voltages V1 and V2 set, and the first time width T1 and the second time width T2 are determined. The time constant τ of the detection signal S0 is determined based on the first and second time widths T1 and T2.

Fig. 11 is a graph showing the discrimination of the scintillator section with respect to the time constant of the detection signal obtained in the measurement experiment shown in fig. 9. In the graph of fig. 11, the horizontal axis represents the fall time τ d (ns) of the detection signal S0 obtained as the time constant τ. In the experimental results shown in fig. 11, it is possible to clearly distinguish between the detection data of the GSO scintillator distributed in the region R1 where the fall time τ d is short and the detection data of the GAGG scintillator distributed in the region R2 where the fall time τ d is long. Such a scintillator determination function can be applied to, for example, determination of a scintillator portion in a Phoswich-type detector configured by superimposing a plurality of types of scintillator portions having different time constants of detection signals, and thus a detection device that can cope with a high count rate and can reduce power consumption can be realized.

Fig. 12 is a view schematically showing the configuration of a third embodiment of the radiation detection apparatus. The radiation detection apparatus 1C according to the present embodiment includes a radiation detector 10C, a time waveform measuring unit 20, and an analyzing unit 30. Among these, the configurations of the time waveform measuring unit 20 and the analyzing unit 30 are the same as those shown in fig. 1. In fig. 12, the display unit 31 and the storage unit 32 connected to the analysis unit 30 and the scintillator 11 included in the radiation detector 10C are not illustrated.

The radiation detector 10C in the present configuration example has the scintillator 11 and the photodetector 15. The photodetector 50 having a plurality of light detection pixels (light detection units) and configured as MPPC is used as the photodetector 15. Fig. 13 is a plan view showing the structure of the photodetector 50 in the radiation detection apparatus 1C shown in fig. 12. Fig. 14 is a partially enlarged plan view showing the structure of the photodetector 50 shown in fig. 13. Fig. 14 shows an enlarged view of the central portion 51 of the photodetector 50 shown in fig. 13.

The photodetector 50 includes N photodetector pixels (micro pixels) 52 arranged in one or two dimensions and each generating a detection signal S0 in response to incidence of light, and a single output terminal 16 for outputting the detection signal S0 generated in each of the N photodetector pixels 52 to the outside. Here, N is an integer of 2 or more. For a specific configuration of MPPC, for example, patent document 1 can be referred to.

In the configuration examples shown in fig. 13 and 14, N light detection pixels 52 are two-dimensionally arranged on the detector chip of the photodetector 50. In addition, a common electrode 58, in which the detection signals S0 from the respective light detection pixels 52 are collected, is disposed in the central portion of the detector chip. In fig. 13, the light detection pixels 52 are illustrated only in the peripheries of both end portions of the detector chip in order to facilitate observation of the common electrode 58 and the like.

Each of the N light detection pixels 52 in the light detector 50 has an Avalanche Photodiode (APD: Avalanche photo diode)53 operating in geiger mode and a quenching resistor 54 connected in series with respect to the APD 53. As shown in fig. 14, the quenching resistor 54 is connected to the common electrode 58 via a signal line 59. The detection signal S0 generated in the light detection pixel 52 is output from the output terminal 16 to the outside via the signal line 59 and the common electrode 58.

The N light detection pixels 52 in the photodetector 50 are configured to output detection signals S0 having different time waveforms (different time constants from each other). In the present configuration example, specifically, the photodetector 50 is configured to have a time waveform for specifying the detection signal in the N photodetection pixels 52 and a quenching resistor 54 having a time constant with a resistance value different from each other.

Fig. 15 is a flowchart illustrating a radiation detection method carried out in relation to the radiation detection apparatus 1C illustrated in fig. 12. In the radiation detection method shown in fig. 15, first, radiation is detected in the radiation detector 10C constituted by the scintillator 11 and the photodetector 50 including the N light detection pixels 52, and a detection signal S0 is output from the output terminal 16 of the photodetector 15 (step S31).

The detection signal S0 is input to the first and second comparators 21 and 22 of the time waveform measuring unit 20 via the amplifier 18 and the branch point 17. The first comparator 21 compares the first threshold voltage V1 with the detection signal S0, and outputs a first digital signal S1 having a first time width T1. In addition, the second comparator 22 compares the second threshold voltage V2 with the detection signal S0, and outputs a second digital signal S2 having a second time width T2 (step S32). These first and second time widths T1, T2 are measured by the first and second time width measuring devices 23, 24, respectively (step S33).

The analysis unit 30 derives a time constant τ indicating the time waveform of the detection signal S0 based on the first and second time widths T1 and T2 measured by the first and second time width measuring instruments 23 and 24 (step S34). The analysis unit 30 determines whether or not the detection signal S0 is a detection signal output from any one of the N light detection pixels (light detection units) based on the obtained time constant τ (step S35).

In the configuration in which the time constant τ of the detection signal S0 is determined based on the first and second time widths T1 and T2 as described above, when the photodetector 50 includes N photodetecting pixels (photodetecting units) 52, it is possible to determine whether or not the detection signal S0 is output from any one of the N photodetecting pixels (photodetecting units) 52 based on the determined time constant τ.

In the present configuration example, the photodetector 50 includes N light detection pixels 52 as described above, but the number of light detection pixels (light detection units) 52 may be arbitrarily set to 2 or more. For example, when the photodetector 5 includes a first photodetector that outputs a detection signal having a predetermined time waveform and a second photodetector that outputs a detection signal having a time waveform different from that of the first photodetector, it is possible to determine whether or not the detection signal S0 is a detection signal output from either of the first and second photodetectors based on the obtained time constant τ.

In addition, as for the configuration of the N light detection pixels 52 that output detection signals of mutually different time waveforms in the photodetector 50, various configurations can be specifically used in addition to the configuration shown in fig. 12.

Fig. 16 is a diagram schematically showing a configuration of a first modification of the photodetector 15 in the radiation detection apparatus 1C shown in fig. 12. In the present configuration example, the photodetector 15 is configured as a photodetector 50A having N number of photodetection pixels 52 and a single output terminal 16.

Each of the N light detection pixels 52 in the light detector 50A has an avalanche photodiode APD53 operating in geiger mode and a quenching resistor 54 connected in series with respect to the APD53, and a frequency filter 55 connected in series between the quenching resistor 54 and the output terminal 16.

In the present configuration example, the photodetector 50A is configured such that the frequency filters 55 in the N photodetection pixels 52 have different frequency characteristics from each other. Thereby, the N light detection pixels 52 in the light detector 50A output detection signals S0 having mutually different time waveforms. Each of the frequency filters 55 in the N light detection pixels 52 is, for example, a high-pass filter, a low-pass filter, or a band-pass filter having mutually different cutoff frequencies.

Fig. 17 is a diagram schematically showing a configuration of a second modification of the photodetector 15 in the radiation detection apparatus 1C in the detection apparatus shown in fig. 12. In the present configuration example, the photodetector 15 is configured as a photodetector 50B having N photodetection pixels 52 and a single output terminal 16.

Each of the N light detection pixels 52 in the light detector 50B has an APD53 operating in geiger mode, a quench resistor 54 connected in series with respect to the APD53, and a capacitor 56 connected in parallel with respect to the APD 53.

In this configuration, the photodetector 50B is configured such that the frequency filters 56 in the N photodetection pixels 52 have different capacitance values from each other. Thereby, the N light detection pixels 52 in the light detector 50B output detection signals S0 having mutually different time waveforms.

The radiation detection apparatus according to the present invention is not limited to the above-described embodiments and structural examples, and various modifications may be made. For example, although the amplifier 18 is provided for the detection signal S0 output from the photodetector 15 in the configuration shown in fig. 7 and 12, the amplifier 18 may not be provided if it is not necessary.

In the above configuration example, the fall time τ d is set as the time constant τ with respect to the time constant τ indicating the time waveform of the detection signal S0 obtained by the analysis unit 30, but other parameters with respect to the time waveform may be obtained as the time constant τ as long as the time waveform of the detection signal S0 can be discriminated. In the above configuration example, the time width of the detection signal S0 used for deriving the time constant τ is the first and second time widths T1 and T2, but may be 3 or more types of time widths, for example.

In the radiation detection apparatus according to the above-described embodiment, the radiation detection apparatus is constituted by: (1) a scintillator that generates scintillation light in response to radiation; (2) a photodetector that detects scintillation light output from the scintillator and outputs a detection signal; (3) a first comparator that compares the first threshold voltage with the detection signal and outputs a first digital signal having a first time width corresponding to a time during which a voltage value of the detection signal exceeds a first threshold; (4) a first time width measuring device for measuring a first time width of the electronic signal; (5) a second comparator that compares a second threshold voltage different from the first threshold voltage with the detection signal and outputs a second digital signal having a second time width equivalent to a time during which a voltage value of the detection signal exceeds the second threshold; (6) a second time width measuring device that measures a second time width of the second digital signal; and (7) an analysis unit configured to obtain a time constant indicating a time waveform of the detection signal based on the first time width and the second time width.

Here, in the above detection apparatus, the scintillator may include: the scintillator includes a first scintillator portion that generates scintillation light having a predetermined time waveform, and a second scintillator portion that generates scintillation light having a time waveform different from that of the first scintillator portion. In this case, the analysis unit may be configured to determine whether or not the detection signal is a detection signal output from the photodetector due to scintillation light generated in either one of the first scintillator unit and the second scintillator unit, based on the determined time constant. In such a configuration, the scintillator portion can be reliably discriminated based on the time constant of the detection signal.

In the above-described detection device, the photodetector may include a first photodetector that generates a detection signal having a predetermined time waveform and a second photodetector that generates a detection signal having a time waveform different from that of the first photodetector. In this case, the analysis unit may be configured to determine whether or not the detection signal is a detection signal output from any one of the first light detection unit and the second light detection unit based on the obtained time constant. In such a configuration, the light detection unit can be reliably discriminated based on the time constant of the detection signal.

As for a specific configuration of the detection device, each of the first time width measuring device and the second time width measuring device may be a configuration including a time-to-digital converter. Thus, the first and second time widths of the detection signal can be appropriately measured.

In the above-described detection device, the condition may be satisfied that the rise time τ r with respect to the fall time τ d in the time waveform of the detection signal satisfies

(τ r/τ d) < 0.1. In the above-described detection device, the analyzing unit may be configured to set the first threshold voltage as V1, the first time width as T1, the second threshold voltage as V2, and the second time width as T2, and to set the first threshold voltage as V1, the first time width as T1, and the second time width as T2

τ＝(T1-T2)/log(V2/V1)

The time constant τ is obtained. With these configurations, the time constant τ of the detection signal can be obtained appropriately.

In the above-described detection device, the analysis unit may be configured to further determine a peak value in a time waveform of the detection signal based on the time constant. According to this configuration, the peak value of the detection signal can be appropriately determined without separately providing a peak value measuring device in the time waveform measuring unit including the comparator and the time width measuring device.

Industrial applicability of the invention

The present invention can be used as a radiation detection apparatus capable of appropriately acquiring and determining time waveform information of a detection signal output from a radiation detector including a scintillator and a photodetector.

Description of the symbols

1A, 1B, 1C … radiation detection devices; 10. 10B, 10C … radiation detectors; 11 … scintillator; 12 … a first scintillator portion; 13 … a second scintillator section; 15 … light detector; 16 … output terminal; 17 … branch point; an 18 … amplifier;

20 … time waveform measuring part; 21 … a first comparator; 22 … a second comparator; 23 … a first time width measurer; 24 … a second time width measurer;

30 … analysis unit; a display portion 31 …; a 32 … storage section; 35 … thermostatic bath; 36 … a radiation source; 38, 38 … oscilloscope; 2a … PET device; 60 … signal processing part;

50. 50A, 50B … photodetectors; region 51 …; 52 … light detection pixels; 53 … avalanche mode photodiodes (APDs); 54 … quenching resistance; a 55 … frequency filter; 56 … capacitor; 58 … common electrode; 59 … signal lines;

s0 … detecting the signal; sp … signal peak; sr … rising signal portion; sd … falling signal section; s1 … a first digital signal; s2 … a second digital signal; v1 … first threshold voltage; v2 … second threshold voltage; t1 … first temporal width; t2 … second time width.